Top Pentagon officials say the U.S. commitment to Afghanistan will not end when the military campaign is over.  They are also predicting U.S. President Barack Obama's decision to send 30,000 additional troops to Afghanistan will inevitably increase the violence and casualties in the country. 

U.S. Undersecretary of Defense for Policy, Michele Flournoy, says President Obama's decision to send 30,000 more U.S. troops to Afghanistan in the next six months and then begin withdrawing them by July 2011 was made only after a lengthy district by district evaluation of the security situation in Afghanistan.

Flournoy says the withdrawal date is not arbitrary and Mr. Obama did not, as she put it, pull the timeline "out of a hat."

She says after the review the administration is convinced the situation in Afghanistan will improve sufficiently in the next 18 months for U.S. and NATO troops to begin transferring security to Afghan forces.

"The conclusion we reached based on that analysis is that July 2011 is a realistic date for us to plan to begin the process of transferring responsibility in some parts of the country," said Michele Flournoy. "We have very high confidence that by that date conditions will permit us to end the surge and begin a gradual and responsible drawdown of U.S. forces."

In addition to the 30,000 U.S. soldiers, other countries have pledged to send another 7,000 troops to Afghanistan.

Flournoy told a conference at the Washington-based American Enterprise Institute she hopes all the new troops will be deployed in the next six or seven months.

Flournoy says even when the military operation is complete, the U.S. commitment to Afghanistan will remain strong.

"We have insured our Afghan partners that our engagement and our assistance will be enduring," she said. "We will not walk away from Afghanistan when the military mission ends.

The Pentagon announced Monday that about 1,500 U.S. Marines are expected to arrive in Afghanistan later this month, the initial elements of the 30,000 troop surge authorized by President Obama last week.

Brigadier General John Nicholson, a specialist in counterinsurgency who just returned from leading troops in southern Afghanistan, says the new forces will be used to protect the civilian population from the Taliban.

"When we look at counterinsurgency the first and critical step is to separate the enemy from the people," said General Nicholson. "In order to do that in some of these critical districts, we lack sufficient ANSF, Afghan National Security Force capacity.  Therefore, we need coalition forces as a bridge to enable the separation to occur."

Nicholson says as new troops are sent to southern and eastern Afghanistan the fighting will intensify. 

"We are going to clear districts that currently have a heavy enemy presence and it is going to increase the violence and sadly that will increase the casualties," he said.

President Obama says the decision to send the reinforcements is designed, in part, to seize the initiative from the Taliban, which has been gaining ground in recent years.